1. Field of the Invention
The present invention relates to temperature control ovens and particularly to those which provide stabilized heat for critical elements of independent circuits.
2. Description of the Prior Art
Thermistors have become a common sensing element in temperature control circuitry. Both negative and positive temperature coefficient types are employed to control circuitry which drives heating or cooling devices. Positive temperature coefficient thermistors have been used directly in series with a heating element to reduce current to the heating element as temperature rises. Some thermistors also have a transition level such that resistance is nearly constant until the transition temperature is reached after which resistance can increase as much as 150 percent per degree centigrade over a limited range. Even the largest temperature coefficients of resistance available are not sufficiently great in response for some purposes and the use of additional circuitry to drive heating devices becomes cumbersome in compact integrated circuits of today.